It is often desirable to be aware of some property (e.g., wavelength, intensity, etc.) of the light associated with an optical apparatus. The term “light ” as used herein, means, as understood by one of ordinary skill in the optical arts, the electromagnetic energy associated with the optical apparatus in question, and is not to be limited to, for example, wavelengths visible to the human eye, which is a definition that can be found in certain dictionaries intended for laypersons. For example, an optical fiber amplifier typically includes a section or length of optical fiber that comprises an active material (e.g., a rare earth or Raman active material). The optical amplifier can receive input light having a first wavelength and, responsive to receiving pump electromagnetic energy having a second wavelength that is different than the first wavelength, can amplify the input electromagnetic energy to provide an optical output. It can be desirable to be aware of one or more of the properties of the input electromagnetic energy, pump light or output light to, for example, monitor the performance of the amplifier. Feedback can be provided responsive to one or more properties of the sensed light so as to adjust one or more performance characteristics of the amplifier.
One way to monitor the performance of the amplifier is to interpose a coupling device, such as, for example, an optical fiber fused coupler, between sections of the amplifier. Such a coupler can include an input fiber arm, and output fiber arm, and a coupled fiber arm, where the coupled arm is usually in optical communication with a detector, such as, for example, a photodetector. To sense input light, the input arm can be spliced to a fiber propagating the input light to be amplified and the output arm can be spliced to a rare earth doped fiber that will amplify the input light. Typically the coupler senses a selected portion (e.g., 1%) of the optical power of the input light.
While an arrangement such as the foregoing can be useful, and is often employed, there can be drawbacks. For example, in certain applications, optical fiber couplers can add cost to an optical apparatus, require a skilled technician to install or fabricate, be cumbersome to employ, or add an additional mode of failure, thus reducing reliability. Improved methods and apparatus would be a welcome advance in the art.